Fujitsu MB90440G CAN question

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Hi

Anyone know if an MB90440G running at 16MHz can support sustained 1Mbps
traffic on all 3 channels simultaneously?

TIA

Geoff



Re: Fujitsu MB90440G CAN question
 
Quoted text here. Click to load it

I do not understand your question?!? Physically, a 16 MHz clock is
sufficient for generating 1 MHz CAN-frequency just use an appropriate
Baudrate prescaler. Maybe you are concerned if the CPU can handle the
interrupt load, i.e. non-CAN-function of this uC.

Regards,
Taso


Re: Fujitsu MB90440G CAN question
Quoted text here. Click to load it
Taso, thanks for the reply.

It is the CAN module which concerns me. If there are three independant CAN
modules, these should then all be able to work simultaneously at 1Mbps.  If,
on the other hand,  the three CAN channels are somehow implemented in a
single hardware module which uses, for instance, polling (as with the
Infineon TwinCAN), there may be a limit to the traffic which can be handled
simultaneously on all channels.

Since the processor is going to be configured as a dedicated CAN peripheral,
the 20 8-byte packets per millisecond it will need to handle should not be a
big problem.

For bit sampling, any clock down to 8MHz will work fine.

Regards
Geoff



Re: Fujitsu MB90440G CAN question
in theory it can, the problem is what are you going to do with the data. Have
you checked that you can get these chips? The fab plant was hit by an
earthquake last june as far as i know they still havent got it running yet.

Re: Fujitsu MB90440G CAN question

Quoted text here. Click to load it
Have
yet.

The data are to be written to a 71V30 dual port RAM feeding an MC8245
processor. The DPR and uC together form a compact, intelligent 3 channel CAN
+ DUART peripheral.

Interesting news about the fab!



Re: Fujitsu MB90440G CAN question

Quoted text here. Click to load it

Au contraire --- I think they will.  1 Mbit/s CAN bus sending 8-byte
CAN packets --> ~ 130 bits/frame (assuming 2.0B, i.e. 29-bit
identifiers) gives you around 7700 frames/ssec. That's roughly 23
messages per millisecond, per CAN port.  

So you're talking about roughly 85% bus occupation there --- unless
you manage to keep operations on all three busses almost perfectly
synchronized, I strongly doubt you'll manage to reach that kind of
throughput.  You have essentially no headroom left to manoeuver.
--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Fujitsu MB90440G CAN question

Quoted text here. Click to load it

Au contraire --- I think they will.  1 Mbit/s CAN bus sending 8-byte
CAN packets --> ~ 130 bits/frame (assuming 2.0B, i.e. 29-bit
identifiers) gives you around 7700 frames/ssec. That's roughly 23
messages per millisecond for the three CAN ports combined.

So you're talking about roughly 85% bus occupation there --- unless
you manage to keep operations on all three busses almost perfectly
synchronized, I strongly doubt you'll manage to reach that kind of
throughput.  You have essentially no headroom left to manoeuver.
--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.
--
Hans-Bernhard Broeker ( snipped-for-privacy@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

Re: Fujitsu MB90440G CAN question

Quoted text here. Click to load it

OK, understood. As Hans-Bernhard said, the busload is very high. At 16 MHz the
shortest timestep is 62,5 ns. How fast can you poll the registers?

Quoted text here. Click to load it

As Hans-Bernhard said it is very difficult at these busloads! Every ~ 43 µs a
CAN-message arrives in the buffer, so you will need a very fast main-loop for
polling them. I think that you'll need a CPU which is driven with +50MHz.

Quoted text here. Click to load it

Complied.





Site Timeline